The present disclosure relates to self-adaptive cements. In particular, the disclosure relates to set cements that are “self-healing,” i.e., formulations that can adapt to compensate for changes or faults in the physical structure of the cement, or which adapt their structure after the setting phase of the cement in the cementing of oil, gas, water or geothermal wells, or the like.
During the construction of wells, cement is used to secure and support casing inside the well and prevent fluid communication between the various underground fluid-containing layers or the production of unwanted fluids into the well.
Various approaches have been developed to prevent failure of the cement sheath. One approach is to design the cement sheath to take into account physical stresses that might be encountered during its lifetime. Another approach is to include, in the cement composition, materials that improve the physical properties of the set cement. Such materials may include amorphous metal fibers to improve strength and resistance to impact damage. Flexible materials (rubber or polymers) may be added to the cement to confer a degree of flexibility on the cement sheath. Nevertheless, the above-described approaches do not allow restoration of zonal isolation once the cement sheath has actually failed due to the formation of cracks, gaps or microannuli.
A number of self-healing concretes are known for use in the construction industry. However, none of these self-healing concretes are immediately applicable to well cementing operations because of the need for the material to be pumpable during placement.
“Self-healing” cements were eventually developed for oil and gas industry applications. These formulations generally contain additives that react and/or swell upon contact with downhole fluids. When cement-sheath deterioration occurs, exposing the cement matrix or cement-sheath surfaces to downhole fluids, the additives respond and seal cracks or fissures, thereby restoring cement-matrix integrity and zonal isolation. Well cements are potentially exposed to several fluid types during service, including liquid and gaseous hydrocarbons, water, brines and/or carbon dioxide. Thus, depending on the anticipated wellbore environment, it would be desirable to incorporate additives that are able to respond to one or more types of downhole fluids.